This invention relates generally to image-forming machines and methods having charger cleaners. More particularly, this invention relates to electrophotographic image-forming machines and methods having activation of a charger cleaner for a corona charger following an arcing fault.
Electrophotographic (EP) image-forming machines are used to transfer images onto paper or other medium. Generally, a photoconductor is selectively charged and optically exposed to form an electrostatic latent image on the surface. Toner is deposited onto the photoconductor surface. The toner is charged, thus adhering to the photoconductor surface in areas corresponding to the electrostatic latent image. The toner image is transferred to the paper or other medium. The paper is heated for the toner to fuse to the paper. The photoconductor is then refreshedxe2x80x94cleaned to remove any residual toner and chargexe2x80x94to make it ready for another image.
EP image-forming machines use chargers for various applications in the image-forming process. In general, sensitizing chargers are used to form the electrostatic latent image on the surface of the photoconductor. Transfer chargers are used to transfer the toner image from the photoconductor to the paper or other medium. Separation chargers are used to separate the paper from the photoconductor.
These chargers have various configurations. However, they share a similar design, namely that of a corona charger. In a corona charger, discharge or corona wires are positioned within a housing. There is at least one corona wire, but usually three or four. A high voltage potential source is connected to the corona wires to generate ions for charging a surface such as a photoconductor. The high voltage source may be direct current (DC) or alternating current (AC) and provides very low current. For DC, the voltage potential of the corona wires is typically in the range of 5 to 11 kva. For AC, the voltage potential is typically in the range of 13,000 to 22,000 volts peak-to-peak.
Many chargers have a gridxe2x80x94a mesh of perpendicular crossing wiresxe2x80x94positioned between the corona wires and the surface to be charged. The grid has an electrical potential or is grounded to control the charging from the corona wires. The electrical potential of the grid is typically in the range of 300 to 900 volts.
The high voltage potential of the corona wires naturally attracts toner, dust, and other particles. These particles build up and contaminate the corona wires and the grid. This contamination causes poor image quality in the reproduced images and may eventually cause the corona wires and grid to no longer be a uniform charging mechanism.
In addition, the particles and contamination can trigger arcing. While most arcing is from the corona wires to the grid, arcing may occur from the corona wires to the housing and to the photoconductor. The arcing effectively disrupts the charging field, thus causing artifacts to appear on the print images. The artifacts include streaks, spots, speckles, and others.
Many EP image-forming machines have a charger cleaner for cleaning the corona wires and/or grid. Some designs vibrate the corona wires, essentially shaking the contamination loose. Other designs pass a cleaning pad over the corona wires and/or between the corona wires and the grid.
Most charger cleaning is done during the power-up and/or self-check cycles of the EP image-forming machine. Additional charger cleaning is done at preselected intervals, usually after certain quantities of prints are made. However, the amount of toner used differs from print to print. Also, environmental factors may affect the rate of build-up and the level of contamination. Some designs clean the charger after a certain amount of toner is used. Other designs attempt to avoid arcing by sensing when conditions favor arcing and then changing the operating conditions of the EP image-forming machine.
These designs are preventative in nature. However, arcing eventually does happen. When arcing does occur, the high voltage potential supply in most designs detects the arc and reports it to the controller of the EP image-forming machine. Depending upon the specific charger causing the arc, a log error is generated or the machine is shutdown. Normal machine operation is reestablished without action regarding the fault. If the source of the arcing has not been removed, additional arcing may occur. If repeated arcing occurs, the controller eventually will lock out the machine and request service.
Generally, an arc is due to contamination of the corona wires. Consequently, an arc, in most cases, indicates the charger needs cleaning. Also, the output image produced from the image frame where the arcing occurred is usually of very poor quality. This poor quality image should be identified and replaced.
Accordingly, there is a need for an electrophotographic image-forming machine that cleans the corona charger after arcing occurs and replaces the poor quality image created by the arcing.
The present invention provides an electrophotographic (EP) image-forming machine and related method having activation of a corona charger cleaner after arcing occurs. The image-forming process stops when arcing occurs. The corona charger is cleaned. Any prints affected by the arcing are disposed. The image-forming process restarts at the image frame where the arc occurred.
In one aspect of the present invention, an EP image-forming machine has a photoconductor operatively mounted on support rollers. A primary charger, an exposure machine, a toning station, a transfer charger, a fusing station, and a cleaner are operatively disposed about the photoconductor. The EP image-forming machine also has a separation charger, a densitometer, microprocessor control, and other features.
At least one of the primary charger, the transfer charger, and the separation charger has a corona charger with a charger cleaning apparatus. The corona charger also has corona wires disposed within a housing, which is made from an insulative material such as a resin or the like. The corona charger may have any number of corona wires. Preferably, the corona charger has three corona wires.
The corona wires connect to a high voltage potential supply, which may be direct current (DC) or alternating current (AC). In DC, the high voltage supply preferably provides a voltage in the range of about 5 to 11 kva. In AC, the high voltage supply provides a voltage in the range of about 13,000 to 22,000 volts peak-to-peak.
The voltage potential in the corona wires creates a charging field for charging a surface, which may be the photoconductor or other medium for electrostatic charging. A corona voltage detection circuit is connected to measure current changes in the high voltage potential supply. The corona voltage detection circuit provides a voltage signal to a microprocessor.
A grid positioned to cover the open end of the housing. The grid is disposed adjacent to the surface and has a preselected electric potential to control the charge laid down on the surface. The grid may be grounded, but preferably is connected to a power supply providing a voltage in the range of about 300 to 900 volts. A grid voltage detection circuit is connected to measure current changes in the power supply. The grid voltage detection circuit provides a voltage signal to the microprocessor
The microprocessor is connected to the corona cleaning apparatus. The corona cleaning apparatus may be any commercially available corona cleaner, an adaptation thereof, and other suitable designs for cleaning the corona charger. Preferably, the corona cleaning apparatus is a pad or the like disposed to pass between and clean the corona wires and the grid.
The microprocessor or other control device monitors fluctuations in the current supplied to the corona wires and the grid. When arcing occurs, the currents of the high voltage potential supply and/or the power supply fluctuate. The corona voltage detection circuit and the grid voltage detection circuit measure the current fluctuations and provide corresponding voltage signals to the microprocessor.
When a voltage signal is received, the microprocessor cycles the EP image-forming machine into a stand-by mode. The microprocessor may have a buffer or other storage to hold the voltage signal until it can be addressed by the microprocessor. The charger cleaning apparatus is activated to clean the charger; namely, the corona wires and the grid. When the cleaning is completed, the EP image-forming machine returns to normal operation.
In another aspect of the present invention, the EP image-forming machine address the poor quality of the image made on the image frame where the arcing occurred. While the EP image-forming machine is in standby mode, the microprocessor or other control unit determines the faulty image framexe2x80x94the image frame where the arcing occurred.
The poor image quality print due to the faulty image frame, and preferably, all the image prints that follow the faulty image frame are removed or otherwise disposed. The machine restarts the EP process at the image frame where the arcing occurred.
The following drawings and description set forth additional advantages and benefits of the invention. More advantages and benefits are obvious from the description and may be learned by practice of the invention.